1. Field of the Invention
The present application relates to an over-current protection device, and a protective circuit board on which the over-current protection device is disposed. The over-current protection device exhibits positive temperature coefficient (PTC) behavior.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The resistance of conductive composite materials having PTC characteristic is very sensitive to temperature variation. The resistance of the PTC conductive composite material remains extremely low at normal temperature, so that the circuit or cell can operate normally. However, when an over-current or an over-temperature event occurs in the circuit or cell, the resistance instantaneously increases to a high resistance state (e.g. at least 102Ω), so as to suppress over-current and protect the cell or the circuit device.
U.S. Pat. No. 6,713,210 disclosed a circuit board with over-current protection function. As shown in FIG. 1, an IC device 2 is placed on a circuit board 1, and a PTC device 3 is surface-mounted on the circuit board 1. The PTC device 3 is a stack structure in which a PTC material layer 6 is laminated between nickel foils (or nickel-plated copper foils) 7 and 7′. The nickel foils 7 and 7′ serve as electrodes for the PTC material layer 6. A nickel plate 4 serving as an external electrode is secured on the upper surface of the nickel foil 7, and an electrode 5 is soldered onto the lower surface of the nickel foil 7′ that is adjacent to the surface of the circuit board 1. The nickel plate 4 and the copper plate 5 are symmetrical with reference to the PTC device 3. The electrode 5 is an electrode section within the circuit board 1, thereby reducing the height of the assembly to meet the requirement of miniaturization.
The PTC device 3 is soldered onto the circuit board 1, and the bonding strength, however, is worse than that by spot-welding. Therefore, the PTC device 3 may be peeled off from the circuit board 1 in sequential assembling process. For example, when assembling the circuit board 1, the nickel plate 4 may bend to be soldered onto the battery. The torque and tension caused by bending may damage the bonding structure between the PTC device 3 and the circuit board 1, or peel off the PTC device 3 from the circuit board 1.
In view of the foregoing, it is demanded to obtain a solution on how to improve the bonding strength between the PTC device and the circuit board to avoid the peeling of the PTC device from the circuit board.